1. Field of the Invention
The present invention relates to a piston pump for use in, for example, a vehicular brake apparatus.
2. Description of the Related Art
Piston pumps of such a type are disclosed in, for example, Japanese kohyo (PCT) Patent Publication No. 2001-501273 and Japanese Patent No. 3278982. Each of the disclosed piston pumps includes a pump housing having a cylinder bore formed therein; a piston which defines a pump chamber within the cylinder bore and is axially reciprocated so as to increase and decrease the volume of the pump chamber; a suction valve provided in the piston, opening when the volume of the pump chamber increases, and closing when the volume decreases; and a discharge valve provided at the discharge side of the pump chamber, opening when the volume of the pump chamber decreases, and closing when the volume increases. The piston is axially reciprocated to thereby increase and decrease the volume of the pump chamber, whereby fluid flows from a suction port to a discharge port.
In the above-mentioned conventional piston pumps, a portion of a flow path connecting the suction port and the suction valve is formed in the piston by means of cutting, resulting in an increase in the cost of manufacturing the piston. Furthermore, a portion of the flow path formed in the piston is composed of radially extending, communicating holes and an axially extending, communicating hole; and burrs may arise at the intersections between the radially extending, communicating holes and the corresponding axially extending, communicating hole. If a process of removing the burrs is required, the cost of manufacturing the piston will increase further. Since a portion of the flow path connecting the suction port and the suction valve is formed in the piston, the flow path may fail to be imparted with a sufficiently large size, potentially resulting in an increase in flow resistance of the flow path.